Biomolecular assays may typically have required a readout signal to determine the success or failure of the experiment. Typically, for example, in prior art biomolecular sandwich assays, the analytes or target molecules to be detected may have been bound between biorecognition molecules (BRMs) and marker molecules. In the past, a positive result (and thus detection of the presence of the target molecule) may have been determined by detection of the readout signal, which in some cases may have been a fluorescent signal. The fluorescent signal may heretofore have been produced by excitation of a fluorophore bound to the marker molecule, such that the fluorophore emitted photons in the visible spectrum (i.e., as the fluorescent signal).
Exemplary prior art biomolecular sandwich assays may have included genomic assays, where the BRMs may have been single-stranded DNA immobilized on the surface of a substrate (e.g., a microbead). Similarly, the marker molecules may have included single-stranded marker DNA bound to one or more fluorophores. In operation, such prior art genomic assays may have involved a first hybridization reaction between the BRMs and the target molecules, if present. (The target molecules may have included single-stranded target DNA of interest in the experiment.) Thereafter, such prior art genomic assays may have involved a second hybridization reaction between the marker molecules and the target molecules, if present.
Other exemplary prior art biomolecular sandwich assays may have included immunoassays, where the BRMs may heretofore have been first antibody molecules immobilized on a substrate. Similarly, the marker molecules may heretofore have been second antibody molecules (alternately, “marker antibodies”) bound to one or more fluorophores. In operation, such prior art immunoassays may have involved a first reaction between the BRMs and the target molecules, if present. (The target molecules may have included target antigen molecules, or analytes, of interest in the experiment.) Thereafter, such prior art immunoassays may have involved a second reaction between the marker antibodies and the target antigen molecules, if present.
In the past, it may generally have been thought that molecular fluorophores can provide useful and/or sensitive methods for the detection of binding events in biomolecular assays. Such molecular fluorophores may heretofore have been used, when bound, to provide a fluorescent readout signal. It may generally have been thought that suitable molecular fluorophores might include, for example, fluorescein, rhodamine dyes, or ALEXA FLUOR® series dyes (such as those manufactured by Molecular Probes, Inc. of Eugene, Oreg.). More recently, quantum dots (QDs) may have been considered for potential uses as fluorophores.
It may heretofore have been generally thought that assay sensitivity, and the ability to detect fluorescent readout signals, depends on an ability to observe an emission from a chosen marker fluorophore. Accordingly, much assay sensitivity research to date may have been largely aimed at increasing the ability to observe emissions from chosen marker fluorophores. Related developments may heretofore have, therefore, included highly sensitive photomultiplier tubes, more efficient photon collection optics, and/or the use of microfluidic systems. One or more of these developments may have sought to maximize detection sensitivity for very low fluxes of photons, possibly as might be emitted from a small area in a microarray or microbead biomolecular assay.
It may now be believed (though it is not essential to the working of the present invention) that the sensitivity in detecting fluorescent readout signals, and indeed assay sensitivity as a whole, may also depend upon an ability to excite the chosen marker fluorophores. Assay detection sensitivity may, therefore, yet be improved by improving the ability to excite the chosen marker fluorophores. Accordingly, it may be desirable to provide an improved method and system for local excitation of specific fluorophores.
It may be thought, though it may not be essential to the working of the present invention, that fluorescent molecules or QDs enter an electronically “excited state” before they are capable of emitting one or more detectable photons in the visible spectrum. It is also believed, though it is not essential to the working of the present invention, higher percentages of excited molecules in a population may lead to a higher absolute number of (detectable) photons being emitted. Although not necessary to the working of the present invention, it may be thought that an increase in the total number of electronically excited fluorophore molecules may directly increase the assay's detection sensitivity to that population of molecules.
Various techniques may heretofore have been used to produce molecular excitation, including the use of thermal energy (heat), electrical stimulation, and/or light absorption. When an emission of a fluorescent signal is the desired effect, the use of light absorption may be a particularly efficient method for exciting molecular fluorophores.
Previously, lasers may have been used to excite fluorophores. Lasers can be relatively intense sources of light and may, therefore, be efficient at exciting molecular dyes. Lasers may, however, emit very narrow bandwidths of visible light, having a specific single polarization. As such, lasers may not be as efficient at exciting random orientations of molecular fluorophores as might be desired.
Now, in biomolecular sandwich assays, it may be advantageous for both the microbeads and the marker molecules to emit fluorescent readout signals in a test positive scenario. In such a contemplated situation, multiple wavelengths of incident light might heretofore have been required to adequately excite both the microbead fluorophores and the marker fluorophores.
Accordingly, there may be a need to provide an improved ability to excite bound fluorophores, and/or to provide for increased numbers of excited bound fluorophores.
There may also be a need to provide an improved ability to excite fluorophores, and/or to provide for increased numbers of excited fluorophores, bound at various orientations.
There may also be a need to provide for an enhanced emission from fluorophores by controllable localized excitation.
It is an object of a preferred embodiment according to the present invention to provide a system and/or method for enhancing fluorescent detection of target molecules.
It is an object of one preferred embodiment according to the present invention to provide a system and/or method for enhancing fluorescent detection of target molecules in a microbead assay.
It is an object of a preferred embodiment according to the present invention to provide a system and/or method which excites the BRM or marker fluorophores (preferably, the marker fluorophores) via a fluorescent signal emitted from the other (preferably, from the BRM fluorophores).
It is also an object of one preferred embodiment according to the present invention to provide a system and/or method which advantageously tailors an emission profile and/or an intensity of one or more QDs to provide for, and/or control, localized excitation of one or more other immobilized fluorophores in the assay.
It is an object of the present invention to obviate or mitigate one or more of the aforementioned disadvantages associated with the prior art, and/or to achieve one or more of the aforementioned objects of the invention.